Electrodeposition of lead



United States Patent N ELECTRODEPOSITION F LEAD Louis Gianelos, Cleveland, Ohio, assignor to The Harshaw Chemical Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application January 13, 1954, Serial No. 403,913

Claims. (Cl. 204-53) This invention relates to electrodeposition of lead and more specifically to lead fluoborate plating solutions containing cooperating addition agents effective to impart to such solutions good throwing power and the capability of producing deposits free from trees and rough areas.

Prior to my invention, numerous addition agents have been used in lead plating solutions for the purpose of preventing treeing and improving the covering power. Among these, perhaps the most successful has been glue but it is not satisfactory because of its poor stability and the narrow current density range in which it is eifective.

It is an object of the present invention to provide cooperating addition agents which are compatible with each other and effective to improve the covering power of the solution and at the same time suppress the tendency to formation of trees and rough areas. A further object of the invention is to provide for good covering over a wide range of current density and to suppress the formation of trees by the use of a solution which is stable over extended periods of time.

In my search for a satisfactory solution, I found that glue is very excellent, but only in its narrow range of current density and no second addition agent was found which would yield good results over a wider range. In the case of aloin which is excellent by itself in improving covering power over a wide range of current density but not effective to suppress treeing, a second addition agent was necessary. Numerous addition agents were tried with aloin but mostly they interfered with its action or were ineffective for extended periods of operation or tended to precipitate out more or less after the solution was used for an extended period.

It has now been found, in accordance with the present invention, that aloin and dibenzene sulfonamide (CsHsSOzNI-ISOzCsHs) are highly compatible, and that dibenzene sulfonamide is at the same time effective to suppress treeing, free from any tendency to precipitate after extended use of the bath and free from any serious interference with the function of the aloin. The dibenzene sulfonamide does influence the action of the aloin in this respect that a somewhat higher concentration of aloin is necessary when dibenzene sulfonamide is used than when aloin is used alone. It is to be understood that aloin by itself is not satisfactory because of the tendency to the formation of trees and rough spots. Under favorable conditions, that is, when quite free from impurities, the bath containing both dibenzene sulfonamide and aloin produces very attractive deposits having a soft satiny sheen whereas a less attractive fiat gray deposit (also subject to treeing) is produced if the dibenzene sulfonamide is omitted. The action of dibenzene sulfonamide is quite specific, naphthalene sulfonates, toluene sulfonamide and the like being inferior, indeed quite unsatisfactory.

The lead fluoborate solutions in connection with which fiiteute i-zlle a-lln195 my n n iea'f ;e zed.may ave; ompo itio follows Range, Preferred,

g./l. g./l.

Pb(BF4)1 200 to 300 250 HBFA 70 to 90 80 H|BO 15 to 30 22. 5 Cathode Current Density (ASF) 20 to 60 40 To the foregoing solutions I prefer to add aloin to the extent of from 0.1 to 0.5 gram per liter and dibenzene sulfonamide to the extent of from 0.5 to 5 grams per liter,

tive at room temperature and will serve to illustrate the invention:

Example I Pb(BF4)2 g./l.. 250 HBFs g /l 30 H3303 g./l 22.5 1 Aloin g /l 0.2

Dibenzene sulfonamide (CsH5SO2NHSO2CsH5) g./l 1.0 Cathode current density (ASF) 30 Example II Pb(BF4)z g./l 200 HBF4 g./l 80 HsBOs g./l 15 Aloin g./l 0.2 Dibenzeue sulfonamide g./l 2.0 Cathode current density (ASF) 30 Having thus described the invention, What is claimed is:

1. A lead fluoborate plating solution containing lead fluoborate, fluoboric acid and cooperating addition agents in amount sufiicient to increase the covering power and suppress the formation of trees, one of said addition agents being aloin and the other thereof being dibenzene sulfonamide.

2. An electrodeposition process comprising electrolyzing a lead fluoborate plating solution as defined in claim 1 at a cathode current density from 20 to 60 amps. per square foot.

3. A lead fluoborate plating solution containing lead fluoborate in concentration from 200 to 300 grams per liter, fiuoboric acid in concentration from to grams per liter, boric acid in concentration from 15 to 30 grams per liter and cooperating addition agents adapted to produce improved covering power and to suppress the formation of trees, one of said addition agents being aloin, present in concentration from 0.1 to 0.5 grams per liter and the other thereof being dibenzene sulfonamide, present to the extent of from 0.5 to 5 grams per liter.

4. An electrodeposition process comprising electrolyzing a lead fluoborate plating solution as defined in claim 3 at a cathode current density from 20 to 60 amps. per square foot.

bf'lead, the same' containing th 'fcillowirl'g ingredients in proportions indicated:

G./l. Pb(BF4) 2 250 HBF4 80 H3303 22.5 Aloin 0.2

Dibenzne sulfonamide csnasomnsogcennn 1.0'

9 Refefences Cited in the 1119 of this paten;

UNITED STATES PATENTS OTHER REFERENCES Mathers et al.: Journal Electrochemical Society, vol; 

1. A LEAD FLUOBORATE PLATING SOLUTION CONTAINING LEAD FLUOBORATE, FLUOBORIC ACID AND COOPERATING ADDITION AGENTS IN AMOUNT SUFFICIENT TO INCREASE THE COVERING POWER AND IMPRESS THE FORMATON OF TREES, ONE OF SAID ADDITION AGENTS BEING ALOIN AND THE OTHER THEREOF BEING DIBENZENE SULFONAMIDE. 